Hydrogen is universally considered a fuel of the future due to environmental advantages over conventional (i.e., fossil-based) fuels.
As reported by N. Z. Muradov and T. N. Veziroglu in “From hydrocarbon to hydrogen-carbon to hydrogen economy” International Journal of Hydrogen Energy 30 (2005)225-237 in the near- to medium-term, hydrogen production is likely to continue to rely on fossil fuels, that are still abundantly available, relatively low cost and with an existing infrastructure for delivery and distribution. However, fossil-based fuels are considered finite, and are the main source of air pollution, producing CO2, NOx, SOx and other pollutants that cause considerable damage to the environment.
In contrast, renewable energy sources, such as landfill gas and biomass that includes wood, agricultural wastes and the like, are considered infinite; they contain appreciable quantities of hydrogen, oxygen and carbon and can be used as a fuel, which is carbon-neutral. Thus, it is considered wiser and more desirable to obtain hydrogen from renewable energy sources.
In principle, hydrogen can be produced from landfill gas (LFG) or biogas via three routes, after preliminary removal of potentially harmful ingredients such as sulfur-, silicon- and halide-containing compounds.
For example, in one method, LFG is first combusted in a turbine or internal combustion engine producing electricity, followed by the electrolytic dissociation of water to hydrogen and oxygen. The use of LFG as a fuel in microturbines for producing electricity is discussed by Penelope G. O'Malley in “Microturbines Provide Big Potential for Opportunity Fuels” Distributed Energy January/February 2004 34-37 with many lessons learned. However, the overall efficiency for converting LFG to hydrogen via this route is less than 20% and it is unlikely to be of practical importance.
In another method, methane is first extracted from LFG and used as a feedstock for hydrogen production via conventional steam methane reforming (SMR) or other processes. This method has been explored in several publications and patents. In WO 2000/004112, Jan. 27, 2000, Hall teaches the process for production of hydrogen-containing gaseous stream from LFG. After methane is separated from LFG, it is catalytically reformed to hydrogen. Janis Keating in “Cheaper Energy by Going to Waste” Distributed Energy 22-25 January/February 2004, describes how methane gas is scrubbed at the landfill, compressed and fed through a pipeline to a BMW plant in South Carolina; where methane is burned as a fuel.
Acrion Technologies Inc. (ATI) has developed a multi-step CO2-Wash™ process for hydrogen production from LFG, as described under the topic, “Landfill Gas to Power with Acrion's CO2 Wash Process.” at website: http://www.acrion.com/Power.htm. First, LFG is cryogenically separated into methane and CO2 stream, then methane is converted to hydrogen via conventional SMR process. Thus, the technical approach according to the methane extraction method is complex, multi-step and energy intensive. In many cases, this method may not be economically and/or environmentally advantageous, especially when the resources are not large enough or the sources are located in remote areas.
In a third method, LFG is directly reformed to synthesis gas followed by carbon monoxide (CO)-shift reaction and hydrogen recovery and purification. At this time, it appears more advantageous to directly convert or reform landfill gas (LFG) into hydrogen gas via the third method, i.e., direct reforming because it obviates the need for costly and energy intensive recovery of methane from LFG. There is a very little information in the literature on the subject of hydrogen production from LFG, biogas, digester gas, or any other bio-derived methane-containing gas via direct reforming.
Muradov et al studied direct reforming of LFG without oxygen and in the presence of oxygen as reported in “Hydrogen Production via Catalytic Processing of Renewable Feedstocks”, Proc. World Hydrogen Energ Conf. Lyon, France, (Jun. 13, 2006). The authors showed that LFG-mimicking gas could be efficiently converted into hydrogen using transition metal-based catalysts.
The technical difficulties associated with the direct catalytic reformation of LFG or biogas stem mainly from two factors. First, there is a presence of potentially harmful impurities, such as, sulfur-, nitrogen-, silicon- and halogen-containing compounds that could easily deactivate catalysts. Second, the gas source is non-uniform. As a result, despite the fact that extensive resources and quantities of LFG and biogas are available, no large-scale commercial hydrogen production process has been implemented yet.
Biomass is another promising renewable resource for a renewable-based hydrogen production. Of particular importance are various agricultural wastes, wood chips, grass, algae, and the like. Such biomass resources represent an immense, practically inexhaustible, inexpensive and environmentally friendly source for the production of hydrogen. Although the energy use of biomass, for example, for heat and electricity generation is a well-established technology, no information is available on sufficiently large-scale biomass-to-hydrogen projects.
Dalai et al in “Catalytic Gasification of Sawdust Derived from Various Biomass,” Energy & Fuels, 17, 1456-1463, (2003) studied catalytic gasification of biomass materials including Cedar, Aspen, cellulose in the presence of CaO catalyst at temperatures up to 850° C. The main products of gasification were hydrogen (H2), carbon monoxide (CO), methane (CH4) and carbon dioxide (CO2). The gaseous product has to be further processed to produce pure hydrogen.
In “Biomass-to-Hydrogen via Fast Pyrolysis and Catalytic Steam Reforming”, Proc. 1996 US DOE Hydrogen Program Review, vol. 1, p. 457, Miami, Fla., (1996) Chornet et al. reported on the development of the process for hydrogen production via fast pyrolysis of biomass with subsequent catalytic steam reforming.
The following patents disclose methods for the production of hydrogen from biomass or solid waste materials.
U.S. Pat. No. 5,795,666 to Johnssen describes a modular power station using biomass material for a fuel source for the production primarily of hydrogen from solar energy and a method of generating electric energy.
U.S. Pat. No. 6,938,439 to Wikstrom et al. provides a system for use of land fills and recyclable materials involving the separation of landfill gas (LFG) into three streams: methane, CO2 and a residue stream that is commercially unsuitable.
U.S. Patent Publication 2004/0265651 to Steinberg describes a combined-cycle energy, carbon and hydrogen production process using carbonaceous materials, including biomass.
U.S. Patent Publication 2006/0024538 to Steinberg describes an integrated plasma fuel cell process from fossil or biomass fuels with minimal carbon dioxide emissions.
The above processes involve energy intensive systems of cleaning landfill gas (LFG), separating LFG into various streams, plasma decomposition processes, use of high temperatures and pressures to achieve the conversion of either LFG or biomass material to hydrogen. There is a need for a simplified, integrated process that combines several disparate waste sources, such as, LFG, a gas and biomass, a solid to increase energy efficiency and produce high purity hydrogen.
The present invention improves upon and overcomes many of the deficiencies of the prior art.